Field of the Invention
The present invention relates to a process for building tyres, and to a tyre for vehicle wheels obtained by said process.
Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified with the name of “beads”, defining the radially internal circumferential edges of the tyre.
Associated with the carcass structure is a belt structure comprising one or more belt layers placed in radial superposed relationship relative to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band is applied at a radially external position to the belt structure, said tread band too being made of elastomeric material like other semifinished products constituting the tyre.
In the context of the present specification and in the following claims, by the term “elastomeric material” it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this composition further comprises additives such as cross-linking agents and/or plasticizers. Due to the presence of the cross-linking agents, this material can be cross-linked by heating, so as to form the final article of manufacture.
In addition, applied at an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads, are respective sidewalls of elastomeric material.
The sidewalls can be incorporated into the tyre structure following two different alternative design schemes, respectively referred to as “sidewalls over tread” (SOT) and “tread over sidewalls” (TOS). In the design scheme TOS, the radially external apices of the sidewalls are axially internal to the side edges of the tread band and generally interposed between the carcass ply/plies and the respective side edges of the belt structure. In the design scheme SOT, the radially external apices of the sidewalls laterally overlap the respective side edges of the tread band and are axially external thereto.
In the most widespread production processes the carcass plies are made starting from an article of manufacture in the form of a continuous strip, consisting of cords of textile or sometimes metallic material, disposed parallel to each other in a matrix of elastomeric material. A section of a length corresponding to the circumferential extension of the carcass ply to be obtained is cut from the continuous strip. The section is wound on the outer surface of a building drum, the opposite ends being mutually spliced so as to form a carcass ply. In turn, said carcass ply is associated with the aforesaid annular anchoring structures to form a carcass structure.
In the same manner, each of the belt layers is in turn made by winding of a section obtained from a semifinished product in a continuous strip, on an auxiliary drum. The belt structure thus formed, possibly already coupled to the tread band, is subsequently picked up from the auxiliary drum for being coupled to the carcass structure.
In order to avoid or limit storage and management of semifinished products, in recent years production processes have been developed in which at least part of the tyre components are made through laying of elementary components on a forming drum.